Some prior land vehicle navigation apparatus calculate a desired navigation route, via fixed road path information stored in a memory, between a start location of the vehicle and a desired destination location. Some of these systems then determine estimated current vehicle position by dead reckoning and/or other vehicle location techniques, and provide audible and/or visual route guidance to the vehicle operator to guide the vehicle along the desired vehicle navigation route. One such prior system is described in co-pending U.S. patent application Ser. No. 07/543,319 to Smith, entitled, "Land Vehicle Navigation Apparatus", which is assigned to the same Assignee as the present invention. Other such vehicle navigation systems are described in the article, "Automobile Navigation Technology; Where is it Going?" by Robert L. French prepared for the, "First Transportation for the Future Conference" held in May, 1988.
Some prior navigation systems illustrate the navigation route, via fixed road paths, which they calculate between a start location and a desired destination. Other navigation systems just provide vehicle maneuver information at various intersections along the calculated navigation route. Some prior systems display in visual highlighted form the progress, actual vehicle travel track, of a vehicle along predetermined road paths which are defined by map information stored in a memory. Some systems such as those mentioned above have been commercially marketed, but they have failed to achieved wide spread commercial success.
One of the problems which must be solved in vehicle navigation systems is how to rapidly convey to the vehicle operator sufficient navigation information, and how this can be achieved without causing any excessive distraction of the vehicle operator while he is driving the vehicle. Audible navigation maneuver instructions may not efficiently provide sufficient navigation information to the driver, and therefore visual navigation display information will also typically be provided. However, some prior visual navigation displays are complex and require a lengthy comprehension time for the vehicle driver. This is not only undesirable but represents a potentially dangerous situation since the vehicle driver may be distracted from his primary function of driving the land vehicle. If only very simple visual displays are provided, such as just illustrating desired turns, then sufficient navigation information may not be provided to the driver, especially if the driver varies from his planned navigation route.
It is often necessary and/or desirable to advise the operator when he has deviated from a desired planned navigation route. Prior systems which have advised the operator when he is off route, typically have not taken into account that sometimes the operator may require additional navigation instructions with regard to resuming his previous route and/or sometimes the vehicle operator may intentionally deviate from the previous route but wants to resumes the route with or without some modification at a later time. In other words, prior systems have not sufficiently taken into account the various reasons why an off course condition occurs, and therefore they do not provide sufficient options to the driver with regard to recovering, in an efficient manner, from an off course condition. Prior systems also typically don't remind the vehicle operator what off route recovery options are available.
In addition, prior systems have not efficiently visually displayed to the vehicle operator the difference between his present vehicle movement and the calculated route such that the operator himself can correct for off route deviations. While some prior systems have visually displayed the desired route, and some of these have also displayed current vehicle position, this has typically not been done in a minimal time comprehension format to permit, without excessive distraction, the vehicle operator himself to correct for off route deviations.